High Heterogeneity of Virus-Neutralizing and RBD-Binding Activities of COVID-19 Convalescent Sera

The parameters of the humoral response are an important immunological characteristic of donors who recovered from COVID-19 and vaccinated individuals. Analysis of the level of virus-binding antibodies has become widespread. The most accurate predictor of effective immune protection against symptomatic SARS-CoV-2 infection is the activity of virus-neutralizing antibodies. We determined virus-neutralizing activities in plasma samples of individuals (n = 111) who had COVID-19 from April to September 2020. Three independent methods were used: conventional with live virus, with virus-like particles pseudotyped with spike protein, and a surrogate virus-neutralization test (cVNT, pVNT and sVNT, respectively). For comparison, the levels of IgG, IgA and IgM antibodies against the receptor-binding domain of the SARS-CoV-2 spike protein were also evaluated. The levels of virus-binding as well as virus-neutralizing antibodies in cVNT and pVNT showed high heterogeneity. A comparison of cVNT and pVNT results showed a high correlation, sVNT results also correlated well with both cVNT and pVNT. To the greatest extent, the level of IgG antibodies correlated with the results of cVNT, pVNT and sVNT. These results can be used in the selection of plasmas that are best suited for transfusion and treatment of acute COVID-19. In addition, data on the virus-neutralizing activity of plasma are important for the selection of potential donors, for the isolation of SARS-CoV-2-specific B-lymphocytes, in order to further generate monoclonal virus-neutralizing antibodies.